Preparation And Visible-light Photocatalytic Properties Of Ternary Composites Based On Ti₃C₂T_x MXene

Energy crisis and environmental pollution have always been two problems that cannot be avoided in the development of human society.However,the development of solar photocatalysis technology has opened a new way to solve these problems.The utilization of solar photocatalytic reaction to treat water pollution can effectively combine environmental protection with water resource recovery and contribute to the sustainable development of society.As the most deeply studied member of the new two-dimensional MXene family,Ti₃C₂T_x has good conductivity,hydrophilicity and unique layered structure,which can promote carrier migration and increase active sites in the photocatalytic reaction process.At the same time,titanium atoms in the material can be used as a titanium source to prepare TiO₂/Ti₃C₂T_x hybrid materials.So Ti₃C₂T_x can be used as a raw material for preparing TiO₂ and as a co-catalyst for photocatalytic reactions.Meanwhile,pure TiO₂ as a photocatalyst has some problems such as high recombination rate of photo-generated electrons and holes and low utilization of visible light,which seriously limit its practical application.Considering the characteristics of structure and property of Ti₃C₂T_x MXene and the main problems of single TiO₂ photocatalyst,we proposed to construct ternary photocatalyst system including BiOBr/TiO₂/Ti₃C₂T_x and Cu₂O/TiO₂/Ti₃C₂T_x.It was anticipated to extend optical absorption range of TiO₂ to the visible light region and inhibit the combination of photo-generated electrons and holes,and further to synergistically improve the visible light photocatalytic properties.In this paper,Ti₃C₂T_x MXene was firstly prepared using Ti₃AlC₂ as a precursor and the mixture of lithium fluoride and hydrochloric acid as the ethant.Then,TiO₂/Ti₃C₂T_x hybrid materials were obtained by hydrothermal and heat treatment under CO₂ atmosphere,respectively.Finally,ternary composite photocatalysts including BiOBr/TiO₂/Ti₃C₂T_x and Cu₂O/TiO₂/Ti₃C₂T_x were prepared.The component,structure and morphology of the photocatalysts were characterized by XRD,SEM,TEM,XPS and EDS.The optical properties of the composites were studied by UV-visible diffuse spectrum and fluorescence spectrum.Rhodamine B solution?RhB?and methylene blue?MB?solutions were used as target pollutants to evaluate the degradation performance of the ternary photocatalysts.And the following conclusions were obtained:?1?The temperature of hydrothermal reaction and CO₂ treatment significantly affected the phase composition and morphology of TiO₂/Ti₃C₂T_x composites.TiO₂/Ti₃C₂T_x hybrid materials with different TiO₂ contents can be obtained by changing the temperature to effectively control the oxidation degree of Ti₃C₂T_x.?2?By constructing heterojunction structure between semiconductors with narrow band gap?Cu₂O and BiOBr?and TiO₂,the light absorption of TiO₂ was extended to visible light region from ultraviolet region.At the same time,owing to the synergistic effects between TiO₂/Ti₃C₂T_x and BiOBr or Cu₂O,the separation of photo-inducted electron-hole pairs was effectively promoted,and the utilization for visible light was enhanced.consequently,the photocatalytic activities of the composites for organic dyes in visible light were significantly improved.?3?Based on the results of structure characterization and photocatalytic performance,the synergistic mechanism of the composite photocatalyst for degradation of organic dyes under visible light irradiation was proposed.First,the excellent conductivity of Ti₃C₂T_x is facilitated to promote the rapid transfer and separation of photo-generated electrons and holes.Furthermore,the type II heterojunctions between TiO₂,BiOBr and Cu₂O were constructed,which could enhance the light absorption for visible light and effectively prolong the life of photo-generated carriers,consequently greatly improving the photocatalytic activity.